Accept options for the rebase command

[keichan34]

Our use case also required -Xtheirs, so I implemented it. Let me know if anything should be updated. I reused utils.getInputAsArray to split arguments and documented the behavior, but if there's a better way to do this let me know so I can fix it. I wanted to do whitespace first, but thinking about interactions between single and double quotes, etc, it just is much easier to delimit by newline.

Closes #114

[peter-evans]

Thank you! LGTM 🚀

I wanted to do whitespace first, but thinking about interactions between single and double quotes, etc, it just is much easier to delimit by newline.

I think what you've done is fine. 👍

[peter-evans]

Released as v3.1.0 / v3